In a network field, as to an optical transport technology of a next generation which is expected to expand applied fields in the future, an OTN (Optical Transport Network), which integrates TDM (Time-Division Multiplexing) data such as Synchronous Optical NETwork (SONET)/Synchronous Digital Hierarchy (SDH) and packet data such as Ethernet, is recommended by the International Telecommunication Union Telecommunication standardization sector (ITU-T).
Regarding the OTN, there is a specification of an Optical channel Data Unit flex (ODUflex) capable of providing a variable bandwidth in response to demand in order to effectively transmit the packet data which is the current primary traffic.
Up until now, there has been discussed a problem of protecting a transmission path with high priority in a case of switching a fault transmission line which can not be switched to a protection transmission path to a normal working transmission path which has lower priority than the fault transmission line.
Patent Document 1: Japanese Laid-open Patent Publication No. 59-175224